Radio access networks (RANs) using different radio access technologies (RATs) are being deployed, and proposed for deployment, in overlapping configurations, leading to an increasingly heterogeneous mobile radio system infrastructure in urban, and even rural, areas. Potentially, this provides a choice of network type to mobile terminals with multi-RAT capabilities. Network operators have identified benefits from simultaneous and alternating usage by interworking between different technologies.
Typically, during development of a new radio access technology, its interoperability with other already available, or future, RATs tends not to be addressed to any great extent until the technology type is reasonably well-defined following adoption of the main proposals. One interoperability aspect relates to notifying a RAN as to which technologies are supported by a mobile radio terminal, sometimes termed a user equipment (UE), and related information (“UE capability information”). To achieve interworking between different RATs, a network node must be able to handle and interpret UE capability information relating to several different technologies and presented in different formats.
A contribution by Ericsson to 3GPP TSG-RAN WG2 #57-bis R2-071328, incorporated herein by way of reference, provides a summary of UE capabilities in Universal Mobile Telecommunications System (UMTS) and related capabilities for Long Term Evolution (LTE). UE capability may include, for example, PDCP capability (such as the type of header compression supported), RLC capability (maximum RLC AM window size, max number of AM entities, etc.), Transport channel capability (max number of channels, received bits, RF capability FDD/TDD (supported bands, UE power class, Tx/Rx frequency separation), Physical channel capability (max number of codes, SF, received bits), UE multi-mode/multi-RAT capability (support of GSM, multi-carrier), Security capability (ciphering/integrity algorithm supported), Measurement capability (need for compress mode for GSM, multi-carrier measurements) and UE positioning capability. UE capability also includes inter-RAT UE radio access capability, such as GSM and GERAN capabilities. 3GPP standard TS 25.331 “RRC Protocol Specification”, incorporated herein by way of reference, also lists UE capability information.
UMTS, one of the 3GPP family of RATs, allows for an explicit query of the capability of a UE. A radio controller (RNC) sends a “UE capability enquiry” message, via the NodeB (eNB), to the UE and receives in response a “UE capability information” message from the UE. The RNC acknowledges reception of the UE capability information message by sending a final “UE capability information confirm” message to the UE. If the capabilities of a UE change during the network attachment, the UE can indicate this to the RNC by sending an unsolicited “UE capability information” message to the RNC, which acknowledges its reception again with a “UE capability information confirm” message. Thus, a capability information transfer may be initiated by the UE or the RNC depending on the circumstances.
In addition to an explicit enquiry of capability information, the UE capability information may be included as a part of several messages within different signalling procedures, as an information element (IE). During the radio resources control (RRC) connection establishment procedure, for instance, the UE capabilities are included in the final “RRC connection setup complete” message, which is sent from the UE to the RNC.
It may be necessary for the serving RNC, to which the UE is attached, to perform handover to a RAN of a different RAT. Handover between different RATs is termed a “vertical handover”. For example, a RNC in a UMTS network might handover to a base station controller (BSC) in a GSM network. If the UE capability information of a UE is already available in the serving RNC, the UE capability information is included in a particular message during the handover signalling in the network. The structure of the UE capability information in the particular message is specified, taking into account the two types of RAT involved. Where other types of RAT are involved, a different structure may be specified.
For RATs other than those described above, similar procedures are involved, with UE capability information being handled as laid down in RAT-specific procedures to permit interworking.